COMPARING INVERTEBRATES
Chapter 29
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Kingdom Animalia
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Two General Groups of Animals
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Multicelluar
Heterotrophic
Eukaryotic
No cell walls
Most are motile
Most reproduce sexually and are diploid
_______________________
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_______________________
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No backbone
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Backbone
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Great size range
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Sea stars, worms,
jellyfish, insects
Fish, amphibians,
reptiles, birds,
mammals
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_____% of all animal
species
What Animals Do To Survive
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___________________________: stable internal environment
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__________________________________: the product or result of a process stops or limits the
process
Evolutionary Trends
A. Specialized Cells, Tissues, and Organs
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As larger and more complex animals evolved, specialized cells joined together to form tissues,
organs, and organ systems that work together to carry out complex functions.
B. Body Symmetry
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____________________ symmetry – parts are arranged in a circle around a central point
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____________________ symmetry – parts are mirror images of each other (left and right sides)
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___________________________ – no definite shape
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Whereas primitive animals exhibit radial symmetry, sophisticated animals exhibit bilateral
symmetry.
C. Cephalization
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Along with bilateral symmetry came the development of _____________________________,
which is the concentration of sense organs and nerve cells in the front (____________________
part) of the body.
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The digestive, excretory, and reproductive structures are located at the back
(___________________________) end.
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Invertebrates with cephalization can respond to the environment in more sophisticated ways
that can simpler invertebrates.
D. Segmentation
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Many animals who exhibit bilateral symmetry also have segmented bodies.
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Segments have often become ___________________________ for specific functions.
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Segmentation allows an animal to increase in size.
E. Coelom Formation
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Germ layers formed early in embryonic development:
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___________________________ (outermost layer)
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___________________________ (middle layer)
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___________________________ (innermost layer)
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The ____________________________ is a fluid-filled body cavity that is completely surrounded
by mesoderm tissue.
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It represents a significant advance in animal evolution because it provides space for elaborate
organ systems.
Types of body cavities:
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___________________________________ do not have a coelom (body cavity) between
their body wall and digestive cavity.
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__________________________________ have body cavities that are partially lined with
mesoderm.
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Most complex animal phyla are __________________________, meaning they have a true
coelom that is lined completely with tissues from mesoderm.
F. Embryological Development
_____________________________: first opening during the embryonic stages of an organism
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___________________________ – blastopore becomes the mouth, and the anus forms
secondarily
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___________________________ – blastopore becomes the anus, and the mouth forms
secondarily
From the Primitive
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No symmetry or radial
symmetry
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No cephalization
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To the Complex
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Bilateral symmetry
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Cephalization with sensory
apparatus
2 germ layers
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3 germ layers
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Acoelomate
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Pseudocoelomate or coelomate
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No true tissues
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Little specialization
Tissues, organs, and organ
systems
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Sessile
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Much specialization
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Motile
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Form and Function in Invertebrates
• Ch. 29-2
• Feeding and Digestion
• The simplest animals break down food primarily through intracellular digestion, but more complex
animals use extracellular digestion.
• In intracellualar digestion food is digested inside the cells.
– The food size must then be smaller than the cells.
– In extracelluar digestion, food is broken down outside the cells.
– The food size is larger than the cells of the organism.
• How does a starfish eat?
• Patterns of Extracelluar Digestion
• Some animals such as cnidarians and most flatworms ingest food and expel wastes through a single
opening.
• Some cells of the gastrovascular cavity secrete enzymes and absorb digested food.
• Other cells surround food particles and digest them in vacuoles.
• More complex animals digest food in a tube called the digestive tract, which may have specialized
regions such as stomach and intestines.
• Respiration: Gas exchange of O2 and CO2
Two key features of all respiratory systems:
• Respiratory organs have large surface areas that are in contact with air or water
• Have ways to keep the gas exchange surfaces moist to allow diffusion to occur
• Respiration
• Circulation
• In an open circulatory system, blood is only partially contained within a system of blood vessels.
• Circulation
• In a closed circulatory system, a heart or a heart-like organ forces blood through vessels that extend
throughout the body.
• The blood stays within these blood vessels.
• Materials reach body tissues by diffusing across the walls of the blood vessels.
• Blood circulates more efficiently in a closed circulatory system.
• Excretion
• The excretory system is responsible for removing waste material and conserving water.
• Waste product is usually nitrogenous, meaning it contains nitrogen.
• This waste is usually in the form of ammonia (NH3), which is very toxic!
• Excretion
• In aquatic invertebrates, ammonia diffuses from their body tissues into the surrounding water
• Terrestrial invertebrates convert:
ammonia  urea (less toxic)
• Some insects and arachnids convert:
Ammonia  uric acid
• Excretion
• Response—Nervous System
• The nervous system gathers information from the environment.
• The simplest nervous system, found in cnidarians, are nerve nets.
• Trends in the Evolution of the Nervous System
• Centralization—nerve cells are more concentrated (ex: ganglia)
• Cephalization—high concentration of nerve cells in the anterior region (head/front)
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Specialization—more developed sensory organs
– To detect light, sound, chemicals, movement, etc.
• Movement & Support
• Most animals use specialized tissues called muscles to move, breathe, pump blood, and perform other
life functions.
• In most animals, muscles work together with some sort of skeletal system that provides firm support.
Three main kinds:
• Hydrostatic skeletons
• Exoskeletons
• Endoskeletons
• Movement & Support
• Hydrostatic skeleton
– No hard structures
– Lacks muscles
– Water filled cavity (gastrovascular cavity)
– Exoskeleton or external skeleton
– Outside the body
– Hard body covering made of chitin
– Has to be shed (molting)
• Endoskeleton
– Structural support inside the body
– Muscles
• Reproduction
• Sexual reproduction is the production of offspring from the fusion of gametes.
– Maintains genetic diversity because it generates new combinations of genes
• Asexual reproduction
– Ex: Fragmentation
– Ex: Budding
– All offspring are genetically identical to parent (clones)
– Allows for organisms to produce offspring faster
– Genetic diversity decreases  less able to deal with changes
– Reproduction
• Some organisms are hermaphrodites, meaning that they produce both sperm and egg.
• Reproduction
Fertilization: unification of sperm & egg
• External fertilization
– Observed in less complex animals
– Eggs are fertilized outside the body
– Gametes are released in surroundings
– Aquatic environment
• Internal fertilization
– Observed in more complex animals
– Eggs are fertilized inside the female’s body
– Require specialized organs